Devices, such as scanners and printers, output device values (like RGB values or CMYK values) depending on the respective devices. To handle device values, a color conversion table (a device profile) for converting device values into device-independent colors is created, and then device values are converted into colorimetric values in a device-independent color space by using the device profile. As an example of a way to create a device profile, a description is now given of a way to create a scanner profile. To create a scanner profile, a chart for creating a scanner profile is output with a printer, and the chart is measured with a scanner and a colorimeter. RGB values obtained by measurement of the chart with the scanner and corresponding L*a*b* values in the CIE 1976 color space or XYZ values of the CIE 1931 color space obtained by measurement of the chart with the colorimeter are associated with each other, whereby a scanner profile is created. With this scanner profile, RGB values obtained by measurement of another color chart (for example, a chart for obtaining a printer condition) with a scanner can also be converted into colorimetric values like L*a*b* values.
In measurement of a chart including an array of patches with a scanner, the scanner can measure not only light reflected on a target patch which is actually measured but also diffuse light coming from patches surrounding the target patch. The degree of the diffuse light (referred to as the level of flare) coming from the surrounding patches depends on color and size of the surrounding patches. Therefore, if a chart for creating a scanner profile is different in composition (color and size of patches) from another chart to be subjected to color conversion, such a difference makes a difference in the level of flare between at the time of measuring the chart for creating a scanner profile and at the time of measuring another chart. It damages the accuracy of color conversion of another chart with a scanner profile.
With regard to a technique to restrict an occurrence of the flare in measurement of a chart, Japanese Unexamined Patent Publication (JP-A) No. 2007-170883 discloses an image forming method for creating a test chart including an array of color areas. The method includes: a step of creating a first image area including areas of colors belonging to a first color group among colors classified according to color component ratio; a step of creating a black image area adjacent to the first image area; and a step of further creating a second image area including areas of colors belonging to a second color group among the colors classified according to color component ratio.
A use of the technique disclosed in JP-A No. 2007-170883 reduces flare which occurs in measurement of the test chart, but a use of the technique for another chart having the different composition may hardly reduce flare which occurs in measurement of the chart so as to bring the level of the flare close to the level of flare which occurs in measurement of the test chart. It may result in failure of improvement of the accuracy of the above-described color conversion with a scanner profile.